The present invention relates generally to glide heads for evaluating glide quality of a disc surface, and to related methods. More particularly, the present invention relates to a glide head with a thermal transducer for detecting defects on a disc surface.
Disc drives are used for storing information, typically as magnetically encoded data, and more recently as optically encoded data, on a disc surface. The storage and retrieval operations generally involve “flying” a read and/or write head over the surface. As storage densities increase, the fly height of the heads over the disc surfaces generally are decreased. Consequently, defect heights on the discs must decrease proportionally to reduce or eliminate contacts between the head and disc that could damage the head, the disc or both.
Glide tests are used to determine if a given disc meets the required glide quality. The glide quality of a disc is related to the disc smoothness, although other defects also may alter glide quality. In particular, tests are used by computer disc manufacturers to control and assure the quality of the disc media. Generally, all hard drive discs are tested before shipment. During a glide test, the test head or slider flies over a disc surface generally at a predetermined clearance from the disc surface, known as the glide height or fly height. The glide head or slider includes a transducer that detects interactions between the disc and the glide head due to defects on the disc surface.
The glide heads are selectively moved under the control of electronic circuitry to any one of a plurality of circular, concentric data tracks on the disc surface by an actuator device. Each slider body includes an air bearing surface (ABS). As the disc rotates, the disc drags air beneath the ABS, which develops a lifting force that causes the glide head to lift and fly above the disc surface. Glide heads generally are designed to have a fly height that is sensitive to the linear velocity of the disc surface relative to the glide head. For example, to detect smaller defects on a disc surface, the disc velocity can be decreased to decrease the fly height of the glide head.
A transducer can be used to detect contacts between the glide head and defects. Generally, piezoelectric transducers are used to detect vibrations that result from contact between a glide head and a disc defect. Using glide heads, the process of mapping disc defects while changing the fly height of the head requires several scans at different head fly heights to map the entire range of defects. As the speed is changed, the response of the specially designed glide head also changes. For example, if the speed is reduced, the energy of the impact is reduced, thus making it more difficult to calibrate to the defect size and height.